Among the majority of bird species males and females breed in monogamous pairs, and it is not uncommon for these pairs to remain stable throughout the reproductive lifetime of the animals. Moreover, both sexes are often heavily committed to the parental care of the young. For instance, in the ring dove both male and female construct the nest, incubate the eggs, and feed the young. The contributions of the two sexes are not merely additive; They complement one another in an exquisitely tuned division of labor. The complexity of this relationship confronts is with several challenging questions which constitute the basis of our research program: (1) To what extent are the basic physiological (e.g., hormonal) changes which carry the male and female through the various stages of the breeding cycle similar or different in the two sexes, and how they are synchronized? (2) Since ring doves develop a preference for particular individuals as mates and since such individual attachments increase the efficiency and productivity of the pair, what factors promote the establishment and maintenance of these social relationships? (3) Because the male invests himself so heavily in parental care, what strategies does he use to ensure that the young produced are, in fact, his own? BIBLIOGRAPHIC REFERENCES: Erickson, C.J. & M.C. Martinez-Vargas. The hormonal basis of co-operative nest building. In Neural and Endocrine Aspects of Behaviour in Birds. Caryl, P., Wright, P., & Vowles, D.W. (Eds.) Amsterdam: Elsevier, 1975, 91-109. Erickson, C.J. and Zenone, P.G. Courtship differences in male ring doves: avoidance of cuckoldry? Science, 192, 1976, 1353-1354.